You need to delete the beta profile (Settings > General > Profiles > iOS 9 Beta > Delete Profile) then put the device in DFU mode and restore using iTunes.

The real issue is that and device backups from 9.1 cannot be used to restore to 9.0.1, so unless you have an archived backup of 9.0.1 or below, you will lose your data. Of course, anything that is stored in iCloud will recover, but nothing else - no app data, no messages, etc that is not stored in iCloud.